This section provides background information related to the present disclosure which is not necessarily prior art.
Direct gas-fired heaters have been manufactured for over 50 years to serve industrial and commercial facilities. In direct fired commercial heaters, circulation air and products of combustion are vented directly into the space being heated, unlike indirect fired heaters that vent combustion products to the outdoors. Direct gas-fired heaters are primarily intended for space heating applications in commercial and industrial facilities to address the heat load and ventilation requirements of these facilities.
Direct gas-fired heaters have also been marketed for over 50 years with a blow-through heater configuration in which the blower is upstream of the burner. More specifically, the blower is located to handle outside air and blow the outside air past a burner, which is operable for heating the outside air before it is discharged into the space to be heated.
Direct fired blow-through heater configurations are well suited for use as space heaters. In this case, a direct blow-through heater may be applied to address the heat load of a facility and not to match a given exhaust application. Industrial and commercial buildings have an infiltration load element as part of its heat load as a result of wind and temperature differences between indoor and outdoor temperatures. Based on ASHRAE (American Society of Heating, Refrigeration, and Air-Conditioning Engineers) ventilation requirements, it is often necessary to provide a source for this ventilation requirement as well as which can be met by this same heater.
In some well insulated buildings, the infiltration element of the heat load analysis can show that the infiltration load and the load associated with the ventilation requirement are more significant than the conduction load. In these applications, the optimization of a heating system occurs when the system first addresses and matches the combination of infiltration load and ventilation load on a designated day and then checks to verify that the conduction load requirement has also been addressed. When a direct fired heater is utilized for space heating, that portion of the heater's capacity that heats the outside air temperature to room temperature is directly tied to the infiltration and ventilation heat load. That portion of the heater capacity above room temperature and the maximum temperature rise of the heater are applied to the conduction load with any extra capacity also being applied to any infiltration and ventilation heat load remaining, if required. There is a significant system efficiency advantage if the blow-through heater is capable of obtaining a temperature rise equal to the maximum discharge temperature allowed by the ANSI (American National Standards Institute) Standard Z83.4 for Non-Recirculating Direct Gas-Fired Industrial Air Heaters. ANSI Standard Z83.4 sets the maximum discharge temperature at 160° F. and limits the maximum temperature rise to 190° F. In an application where the minimum design for a location is 0° F. (e.g., like Saint Louis, Mo., etc.), a heater with a temperature rise of 160° F. would therefore optimize the heater selection for that location.
Another benefit of a direct fired blow-through space heater configuration is that a space heater is generally cycled on and off based on a call for heat by a room thermostat. A conventional draw-through make-up air heater will run continuously as long as the exhaust fan is operating. During the operating time of a space heater, the heater airflow tends to neutralize the flow of infiltration air into the building as a result of the air brought in by the heater escaping out of the same cracks. This exhale of the air supplied by the heater carries out other contaminants that may be created in the building. If the infiltration rate of the building is too low, additional relief openings may be required to meet the minimum ventilation requirements of the facility.
Air conditioning may be used to alter the properties of air to more favorable conditions, typically with the aim of distributing the conditioned air to an occupied space to improve comfort. Commonly, air conditioning lowers the air temperature through cooling, although other conditioning effects may also be implemented. The cooling is typically done using a refrigeration cycle (sometimes including direct expansion coiling), but other suitable technologies may also be used.
Energy recovery ventilation is the energy recovery process of exchanging energy contained in normally exhausted building or air space air and using it to treat (precondition) the incoming outdoor ventilation air in residential and commercial heating, ventilation and air conditioning (HVAC) systems. During the warmer seasons the system pre-cools and dehumidifies, and during the cooler seasons the system pre-heats and humidifies.
The inventors have recognized that a combination of blow through direct fired heating systems, direct expansion cooling, and energy recovery ventilation may allow for increased energy efficiency, as well as improving indoor air quality. The inventors have also recognized that combining the evaporator coil of an air conditioning system with the air flow of a direct fired system can lead to formation of harmful products of combustion (e.g., phosgene gas) due to the possible combustion of refrigerants as they pass the flame of a direct fired system.